1. Technical Field
The present invention relates to a coupling structure for a multi-layered chip filter and a multi-layered chip filter with the structure.
2. Description of the Related Art
Recently, as a mobile communication terminal and a wireless communication device are rapidly increased, a low temperature co-fired ceramic (LTCC) chip filter excellent in view of performance, size, reliability, cost, and the like, has been widely used together with a surface acoustic wave (SAW) filter as a band pass filter (BPF), which is a necessary component for the mobile communication terminal and the wireless communication device.
Generally, LTCC indicates a process technology in which a metal and a ceramic substrate thereof are co-fired at a low temperature and a resultant product thereof. A high-temperature firing method through dielectric ceramic according to the related art should use a high-cost metal such as Pt, Pd, and the like, in view of characteristics thereof. However, this metal has a disadvantage in that it has a large transmission loss in addition to cost side.
However, when using a glass-based material or a ceramic in a form mixed with the glass-based material, substrates coated with a metal may be compressed and fired at about 800 to 1000° C. and also has excellent high-frequency characteristics.
The LTCC method may be used to configure a thin-film multi-layer circuit and in particular, is advantageous in implementing an element having a large size such as an inductor. For example, it is difficult to dispose the inductor over a chip die such an MMIC, a RFIC, or the like, due to its large size. However, when the LTCC method is used, it is possible to dispose the inductor under the chip and also dispose elements to be disposed outside under the chip in a thin film form, thereby making it possible to save a space.
It is possible to fabricate internal elements integrated in the MMIC/RFIC as described above as well as general multi-layered unit passive elements such as C, L, and the like, or fabricate passive elements such as a chip coupler by using the LTCC process.
Generally, a structure of a multi-layered filter configured as a multi-layer through the LTCC process, and the like is configured to include resonator layers 20 and 40, a coupling layer 30 and a ground layer 10 as shown in FIG. 1A. A basic equivalent circuit of the structure shown in FIG. 1A is shown in FIG. 1B.
Meanwhile, in order to improve skirt characteristics or attenuation characteristics through adjustment of an attenuation pole, the multi-layered filter having a coupling inserted between resonators or between input and output ends is widely used, as shown in FIG. 1.
FIG. 2 shows a change in frequency characteristics of a filter due to use of a coupling 31 through a high-frequency three dimensional simulation. It may be appreciated in FIG. 2 that the skirt characteristics and the attenuation characteristics are improved, the attenuation pole is moved to a low frequency, a pass bandwidth becomes narrow, and the phenomena as described above are intensified as an overlap area between the coupling 31 and resonator 41 becomes large.
However, improvement of the attenuation characteristics and movement of the attenuation pole may be limited due to reduction of the pass bandwidth according to increase of the coupling area.